Problems with Polling Iowa Caucus Goers

This article from Jay Cost at Real Clear Politics explains why it is hard to find accurate polls of Iowa caucus goers...

A poll of Iowa Democratic caucus goers does not really mimic the process in which they participate. In a general election - you go into a voting booth, select your first choice, leave the booth, and drop the ballot in the box. And so, a poll that asks you for your first choice and then moves on to other questions does a reasonably good job of mimicking the act of voting.

However, this is not the experience of Democratic caucus goers. Iowa Democrats begin by standing in an area designated for their first choice candidate. Then, for thirty minutes, they either persuade or are persuaded by others to switch their choices. At the end of the half hour, electioneering is halted and caucus officials count the number of supporters that each candidate has. Candidates who have less than 15% or 25% are deemed not to be viable. And so, another thirty minutes for electioneering is once again granted. The supporters of nonviable candidates must find new candidates to support, team up with supporters of other nonviable candidates to make their candidate viable, or abstain.

The longtime Iowa voter probably knew this already, but the article goes much more in depth and worth looking over.